The purpose of this project is to study immune responses in man and experimental animals to natural and experimental rickettsial infections. Currently, we are studying chronic Q fever in man. Studies have involved isolation and characterization of Coxiella burnetii isolates from heart valves and the characterization of the immune response in chronic Q fever. We are also investigating the immune responses in man and experimental animals to natural and experimental infections of Legionella pneumophila, the causative agent of Legionnaires' disease (LD). This past year we compared suitability of various antigen preparations in the microimmunofluorescence test (micro-IF) and initiated a study of serological typing of strains of L. pneumophila using mouse antiserum. We also devised an ELISA test for measuring antibody responses in LD patients and to experimental infection in guinea pigs.